1. Field of Invention
This invention is related to halftone images.
2. Description of Related Art
Moirxc3xa9 effects occur when two periodic structures of nearly the same period are superposed. As a result, a new family of periodic structures with a larger period appears. The simplest and most noticeable moirxc3xa9 pattern can be seen when two line screen patterns are superposed and oriented at a small angle relative to each other.
The moirxc3xa9 effect can be interpreted as the result of interference between the two image components that have slightly different spatial frequencies. A halftone image generated by a screening technique possesses a strong image component at the halftone screen frequency. When a previously halftoned image is used as the input for a new halftone process, a moirxc3xa9 pattern might occur if the second halftone screen has a frequency close to the frequency of the original halftone screen.
The methods and systems of this invention use negative feedback to reduce moirxc3xa9 effects in halftone images. By determining the difference between an input image and the output image after halftoning, and subtracting the low-frequency part of the difference from the original input image, the moirxc3xa9 effects can be reduced.
As with the black-and-white process, the same basic principles can be extended to color images for reduction of moirxc3xa9 effects within certain color channels and between multiple color channels.
This invention provides systems and methods that reduce moirxc3xa9 effects in black-and-white halftone images.
This invention separately provides systems and methods for reducing moirxc3xa9 effects in color halftone images.
This invention separately provides systems and methods for reducing moirxc3xa9 effects that occur between color channels of a color halftone image.
These and other features and advantages of this invention are described in or are apparent from the following detailed description of the exemplary embodiments.